Sound attenuating structure

Abstract

Sound attenuating structure including a combination of one or more core layers comprising cells directed perpendicular to the main surface of the structure. The core layers are separated from each other by perforated separating sheets, a closed sheet is adhered to one side of said combination and a perforated sheet to the other side of said combination, at which side the sound waves impinge upon the structure. The passages in said last mentioned sheet as well as in the separating sheets have an asymmetric cross section having its smallest diameter somewhat less than the sheet thickness of the structure and increasing from this diameter fluently towards both surfaces of the respective sheet.

We claim: 
     
       1. Sound attenuating structure including a core layer comprising hoenycomb shaped cells directed perpendicular to the main surface of the structure, a closed sheet at one side of said core layer and a perforated sheet at the other side of said core layer, at which side the sound waves impinge upon the structure, characterized in that the passages in said last mentioned sheet have a cross section presenting its smallest diameter somewhere within the sheet thickness of the structure and increasing from this diameter towards both surfaces of said sheet. 
     
     
       2. Sound attenuating structure including a core layer comprising honeycomb shaped cells directed perpendicular to the main surface of the structure, a closed sheet at one side of said core layer and a perforated sheet at the other side of said core layer, at which side the sound waves impinge upon the structure, characterized in that the passages in said last mentioned sheet have a cross section presenting its smallest diameter in that half of the layer thickness directed to the outside of the structure and increasing from this diameter towards both surfaces of said sheet. 
     
     
       3. Sound attenuating structure including a combination of a number of core layers comprising cells directed perpendicular to the main surface of the structure, which core layers are separated from each other by perforated separating sheets, a closed sheet at one side of said combination and a perforated sheet at the other side of said combination at which side the sound waves impinge upon the structure, characterized in that the passages in said last mentioned sheet as well as in the separating sheets have a cross section presenting its smallest diameter in that half of the structure directed to the outside of the structure and increasing from this diameter towards both surfaces of the respective sheet. 
     
     
       4. Sound attenuating structure according to claim 1, characterized in that viewed in the longitudinal passage direction said passages have a symmetrical or asymmetrical double conical cross section with fluent transition. 
     
     
       5. Sound attenuating structure according to claim 1, characterized in that in transversal direction said passages have a circular or approximately circular cross section.